Geochemists only: why do felsic minerals melt at lower temps than mafics?

Question

It doesn't seem right since the high silica minerals have lots of strong covalent bonds, and the mafics have some weaker ionic bonding.

Answer 1

You have it backwards
Covalent bonds are weak bonds like sugar they melt quickly
Ionic bonds are very strong like salt and melt at high temps

Answer 2

Mafic minerals (left side of Bowen's Reaction Series) form simple structures at high temperatures and more complicated structures at low temperatures. The simple minerals (olivines and pyroxenes) react with the melt to produce more complicated minerals (amphiboles and biotites) as the temperature decreases. Mafic rocks also are rich in calcium plagioclase feldspar and poor in sodium plagioclase feldspar (the right side of Bowen's Reaction Series) contained in felsic rocks, and contain almost no potassium feldspars. Calcium plagioclase forms at higher temperatures than do alkali feldspars, probably due to the +2 valence of calcium and the +1 valence of sodium and potassium. It stands to reason that if a mineral forms at high temperatures then it melts at high temperatures. Also, if a mineral forms at low temperatures then it melts at low temperatures.